(1) Field of the Invention
The present invention relates to a suscepter used in the gas-phase epitaxy of compound semiconductor (indium, gallium, arsenic and phosphorus are used), as well as to a process for production of said suscepter. More particularly, the present invention relates to a suscepter which has no pores on the surface and thereby generates no impurity and which causes no cracking when used at high temperatures, as well as to a process for production of said suscepter.
(2) Description of the Prior Art
Gas-phase epitaxy is also called "CVD" ( Chemical Vapor Deposition) and is one of the thin-film formation techniques used in the production of semiconductor elements. In the gas-phase epitaxy, a gas-phase chemical reaction is conducted to form a thin film directly on a semiconductor substrate.
In the gas-phase epitaxy, a thin layer of a semiconductor material is formed epitaxially on a semiconductor substrate by thermal decomposition or a hydrogen reduction reaction of a gaseous component at a high temperature. In this case, the semiconductor substrate must be heated. In general, the semiconductor substrate is mounted on a heating substrate (a suscepter) and is heated via the suscepter.
When gas-phase epitaxy is conducted as above, the properties of the epitaxial layer obtained are controlled by the material constituting the suscepter used. Therefore, the material of the suscepter is a very important factor in gas-phase epitaxy.
As the material of the suscepter, there have been used silicon, molybdenum, tungsten, graphite, etc. Each of these materials is insufficient in stability at high temperatures and also has a problem in purity, and has not been satisfactory. That is, for example, graphite has pores on the surface and easily adsorbs gases, and emits harmful gases during epitaxial operation; and molybdenum and tungsten adversely affect, per se, the respective products obtained, even when they have high purities.
Currently, there is used, as the material of the suscepter, a graphite material comprising a graphite substrate and a silicon carbon (SiC) film formed thereon by CVD. However, since there is a difference in thermal expansion coefficient between the graphite substrate and the SiC film, the graphite material, when used at high temperatures (1,300.degree.-1,700.degree. C.), causes cracking, which invites staining of semiconductor with impurities.